This invention relates to system for interconnecting optical circuit boards with optical connectors, which are arrayed (row or column) on a mounting panel.
For a variety of reasons, modern communication equipment is now being designed to process data at progressively higher speeds. Perhaps the most significant reason relates to the desire to transfer video information between computers. Such data transfer has grown exponentially in recent years because of the Internet, and no decrease in growth is anticipated in the foreseeable future. In order to handle this growth, only optical circuitry appears capable of meeting the demand because of the enormous bandwidth that an optical fiber can provide. Nevertheless, distribution equipment is still needed to route optical signals to the same locations, and this means that optical connecting hardware needs to be sufficiently small to accommodate large numbers of individual fiber connections.
One particular location where congestion occurs is on circuit boards that contain optical components (i.e., optical circuit boards) where individual input/output ports must be provided to make connections on a per-fiber basis. Moreover, it is desirable to plug these circuit boards into a panel, or backplane, that accommodates a number of other circuit boards similar to the way electrical circuit boards are mounted in an equipment bay. However, electrical circuit boards can tolerate substantial displacement in the X, Y and Z directions while still providing reliable electrical connections, but optical circuit boards cannot. (It is noted that the X, Y and Z directions are mutually orthogonal, and that the Z direction coincides with the general direction of signal flow through the connection). Indeed, the primary vehicle for optical connection is the xe2x80x9cbuttxe2x80x9d connector where the end face of one fiber is pressed against the end face of another fiber. In such a connection, there should be no air gap between the fiber end faces and there should be no fiber displacement in the X and Y directionsxe2x80x94otherwise there would be too much signal loss. (It is noted that a singlemode optical fiber has a light-carrying region that is only about 8 microns (xcexcm) in diameter, and that it must be precisely aligned in an axial direction with another fiber.) It is therefore a challenging task to provide a number of optical devices on a plug-in optical circuit board that accurately mate with a corresponding number of stationary optical connectors.
Optical devices are known that might be adapted to mount on an optical circuit board, but their construction is relatively complex and/or their attachment to an optical circuit board requires expensive and time-consuming manual labor. More importantly, there is a need to standardize the optical interface for plug-in optical circuit boards. The interface should provide accurate optical alignment and be suitable for high density interconnections.
The present invention is for an interconnection system that enables an optical circuit board, having a number of optical devices, to be easily connected to and disconnected from a backplane. The optical devices are positioned along a side edge of a generally planar surface of the circuit board and are adapted to interconnect with a like number of optical plugs that are arrayed on the backplane in a row or column. Each of the plugs includes a ferrule having an end face that projects from a connector end of the plug. The front-end portion of each optical device is a jack receptacle that includes: (i) a cavity having a generally rectangular opening for receiving the optical plug, (ii) a boss that extends into the cavity for receiving the ferrule, and (iii) an optical plane where the end face of the ferrule resides when installed within the boss. All of the jack receptacles are positioned on the circuit board such that their individual optical planes are substantially coincident with each other and are parallel to the side edge of the circuit board. The optical plugs and jack receptacles are arranged to engage, but not interlock with, each other.
In an illustrative embodiment of the invention, the ferrules are cylindrical and enclose a single optical fiber. Additionally, the jack receptacles are molded from a plastic material as a single part and include two or more downward-extending pins that are received in corresponding holes in the circuit board for accurate positioning. Accurate positioning is important because plug-in circuit boards make xe2x80x9cblindxe2x80x9d connections, which is to say that the installer is generally unable to see the connection being made during installation and is, therefore, unable to make minor positional adjustments to facilitate connection.
In one illustrative embodiment of the invention, the back-end portion of the edge-mounted optical device also includes a jack receptacle and thus forms a coupling device for interconnecting a pair of optical plugs. Alternatively, the back-end portion of the optical device may include one or more transducers for converting optical signals into electrical signals and/or electrical signals into optical signals.
Plug-in circuit boards that house optical components will soon be as familiar as circuit boards that house electrical components. The plug-in concept has been widely accepted because such circuit boards provide a large and manageable amount of hardware on an easily replaceable device. Circuit boards frequently include diagnostic hardware and software that can alert service personnel when a board is not working properly. And because a defective board can be quickly replaced by pulling out one circuit board and plugging in another, maintenance is facilitated and downtime is minimal. This is particularly useful in large and complex systems where removal of a single board affects a large number of customers. The convenience of plug-in circuit boards is largely attributable to the fact that all connections between the board and a backplane can be non-destructively severed by merely pulling the circuit board from the slot where it operatively resides. By xe2x80x9cbackplanexe2x80x9d is meant, generally, a wall that separates internal apparatus from external apparatus, and through which a connection(s) is made.
In the present invention, the backplane comprises a mounting panel with optical plugs installed in one side and optical circuit boards installed in the other. In particular, the optical circuit boards only use jack receptacles affixed to the edge of the circuit board for making connection to the backplane, which contains an array (row or column) of optical plugs. Unlike prior art interconnection systems, a transceiver device can now be edge mounted on the optical circuit board with its jack receptacle positioned to receive an optical plug, thereby eliminating the need for additional optical jumpers and adapters on the circuit board. And whereas known optical plugs and jack receptacles individually interlock when connected, the present invention avoids individual interlocking of the optical plugs and jacks to facilitate removal of the optical circuit boards from the backplane.